Electronic flashlight units

ABSTRACT

In an electronic flashlight unit, a controlled semiconductor rectifier is ignited simultaneously with the ignition of flash tube and power from a first capacitor flows therethrough. A voltage of one polarity thereby appears across the rectifier. The discharge causes a voltage drop across a resistor and that voltage drop is used to charge an integrating capacitor in correspondence with the integral of the flash light flux as detected by a photoresistor. At a predetermined integral value a switching action applies the voltage of a quenching capacitor across the rectifier in a manner such that the polarity is opposite to said one polarity. The rectifier is thereby turned off to ensure that the flash tube is quenched. In one embodiment two semiconductor rectifiers each connected in series to a reactor are provided in the flash discharge circuit and a second pair similarly connected in the quenching circuit to enable the use of inexpensive low-power semiconductor rectifiers protected from overloading.

[ Apr. 30, 1974 ELECTRONIC FLASHLIGHT UNITS [75] Inventor: Wolfgang Ludloff, Porz-Westhoven,

Germany [73] Assignee: Multiblitz Dr. Ing. D. A.

- Mannesmann GmbH & Co. KG,

Westhoven, Germany [22] Filed: Apr. 26, 1971 [21] Appl. No.: 137,411

[30] Foreign Application Priority Data May 5, 1970 Germany 2021880 Aug. 5, 1970 Germany 2038859 [52] U.S.CI .I 315/158, 315/241 P [51] Int. Cl. H05b 39/04 [58] Field of Search 315/199 C, 158, 151 C, 315/241 P [56] References Cited UNITED STATES PATENTS 3,591,829 7/1971 Murata et a1. 315/151 3,612,947 10/1971 Dennewitzw, 315/151 3,703,662 11/1972 Dennewitz et a1. 315/241 P X 3,229,158 1/1966 Jensen 315/158 3,510,750 5/1970 Horino et al..... 315/158 X 3,344,310 9/1967 Nuckolls 315/158 X 3,344,311 9/1967 Nuckolls 315/158 X Primary Examiner-Nathan Kaufman Attorney, Agent, or Firm-Darbo, Robertson &

Vandenburgh 57 ABSTRACT In an electronic flashlight unit, a controlled semiconductor rectifier is ignited simultaneously with the ignition of flash tube and power from a first capacitor flows therethrough. A voltage of one polarity thereby appears across the rectifier. The discharge causes a voltage drop across a resistor and that voltage drop is used to charge an integrating capacitor in correspondence with the integral of the flash light flux as detected by a photoresistor. At a predetermined integral value a switching action applies the voltage of a quenching capacitor across the rectifier in a manner such thatthe polarity is opposite to said one polarity. The rectifier is thereby turned off to ensure that the flash tube is quenched. In one embodiment two semiconductor rectifiers each connected'in series to a reactor are provided in the flash discharge circuit and a second pair similarly connected in the quenching circuit to enable the use of inexpensive low-power semiconductor rectifiers protected from overloading.

14 Claims, 2 Drawing Figures PATENTEB APR 301914 SHET 2 [1F 2 WOLFGANG LII/0L OFF INVENTOR 1 a ELECTRONIC FLASHLIGHT UNITS BACKGROUND AND SUMMARY OF THE INVENTION This invention relates to an electronic flashlight unit, in which a gas-filled flash tube connects to a supply voltage, preferably a storage capacitor, and is provided with an ignition electrode for releasing a flash discharge. A photoelectric detector controlled by the light reflected from the object is provided, furthermore, it includes an integrating element for the at least approximate integration of the light flux and a quenching circuit for quenching the flash discharge when a given light flux integral is reached. In the prior electronic flashlight units, quenching of the flash discharge is accomplished by supplying a voltage in opposition to the charging circuit of the flash tube to the supply voltage, so that the flash tube has its polarity changed and the flash discharge is quenched. To this end, a capacitor is r provided which is discharged through a controlled rectifier and whose discharge current supplies a voltage opposed to the supply voltage, and of same or greater amplitude than the supply voltage, to the discharge circuit through a resistor or a transformer. This requires a capacitor of relatively high capacity as. the gas in the flash tube still remains ionized for a certain time, also after termination of the flash discharge. If after too short a time the voltage from the storage capacitor is again applied to the flash tube, another ignition of the flash tube may occur due to this residual ionization. Therefore, the capacitor must be of such high capacity to enable it to maintain the voltage of opposite polarity for a time which is greater than the deionization time of the flash tube. It is an object of this invention to improve an electronic flashlight unit of the type indicated in such a manner that the deionization time of the flash tube is no longer of significance and the necessity, resulting therefrom, of a relatively large auxiliary capacitor is eliminated.

It is another object of this invention to design an electronic flashlight unit of the type indicated for high capacities using nonexpensive components.

According to the invention thisis achieved by connecting a controlled semiconductor rectifier in series to the flash tube, said semiconductor rectifier being ignited simultaneously with the flash tube, and that by a quenching circuit the voltage dropping across the controlled semiconductor rectifier can be changed in polarity temporarily.

Thus, by the invention quenching of the flash discharge is no longer accomplished by quenching the flash tube itself by a temporary removal of the supply voltage. Rather a controlled semiconductor rectifier (thyristor) is connected in series to the flash tube. This controlled semiconductor rectifier is ignited together with the flash tube, so that it does not affect the normal flash discharge. Quenching of the flash discharge is accomplished by temporarily changing the polarity of the voltage across the semiconductor rectifier, so that the latter blocks the current flow. Such a semiconductor rectifier has a substantially shorter relaxation time so that by a relatively short change in polarity of the voltage a complete quenching of the semiconductor rectifier is accomplished and therewith, of course, the flash discharge also is interrupted, without any dependence on the deionization of the flash tube itself.

The invention may be realized in such a manner that the quenching circuit includes an auxiliary capacitor adapted to be charged through decoupling resistors and to connect to a first part of the discharge circuit comprising the first controlled rectifier, through a second controlled rectifier controlled by the integrating element, and that is with a polarity opposed to the polarity of the voltage dropping across this part of the discharge circuit during normal discharge.

According to the invention, this further object is solved by providing that in series-connection to the flash tube in the part of the discharge circuit whose polarity can be changed by the quenching circuit, instead of a controlled semiconductor rectifier there is arranged the parallel circuit of two controlled semiconductor rectifiers, each in series to an inductive reactor, and the two controlled semiconductor rectifiers are ignited simultaneously with the flash tube.

The invention starts from the knowledge that the price of controlled semiconductor rectifiers increases disproportionately to the capacity for which these controlled semiconductor rectifiers are designed. Thus, a high capacity can be realized more readily by two parallelly connected controlled semiconductor rectifiers. In practice, however, it shows that due to the inevitable differences in the ignition points of the two semiconductor rectifiers, by simple parallel connection a respective one of them would have applied thereto the full current peak at the moment of ignition, whereby an overloading of this one controlled semiconductor rectifier would be caused. The invention is based on the knowledge that these difficulties encountered in a parallel connection of two conjointly ignited controlled semiconductor rectifiers can be avoided by a seriesconnection of an inductive reactor to each of these controlled semiconductor rectifiers. Such a reactor dampens the current peak at the moment of ignition, so that a strong load on the two controlled semiconductor rectifiers is not applied than before the two rectifiers have been ignited positively. Besides, the discharge of the inductive reactors which practically constitute strictly inductive resistors is not affected as the discharge is substantially of direct current nature after ignition of the flash tube.

In a further modification of the invention, one can proceed similarly with the quenching circuit: Provision can be made that the quenching circuit includes a second pair of controlled semiconductor rectifiers each of which is in series-connection to a reactor and a capacitor is connected parallelly to one each of the controlled semiconductor rectifiers in the discharge circuit of the flash tube, that each of the capacitors connects to the supply voltage through decoupling resistors, and that the controlled semiconductor rectifiers of the quenching circuit are simultaneously ignited by the integrating element when a given light flux signal is reached. It is particularly advantageous, if the capacitors of the quenching circuit are connected with one side respectively between the controlled semiconductor rectifier in the discharge circuit and the associated reactor. For the discharge of the capacitors in the quenching circuit another circuit is connected parallel to the circuit through which the capacitors discharge after ignition of the controlled semiconductor rectifiers through the integrating element and effect the change in polarity of the voltage across the controlled semiconductor rectifiers in the. discharge circuit, said other circuit being closed through the flash tube. The arrangement of the inductive reactors between the capacitors and the flash tube render the said circuit for the capacitor charge relatively high-ohmic, so that the capacitor charge can practically be fully utilized for the change in polarity of the controlled semiconductor rectifiers in the discharge circuit.

The quenching circuit may include another controlled semiconductor rectifier which connects to a capacitor charged by the supply voltage through a resistor. The connection point between the semiconductor rectifier and resistor is then connected through one respective further resistor with the control electrodes of the two semiconductor rectifiers of the second pair. The further controlled semiconductor rectifier can then be controlled directly by an integrating element. The integrating element may include two capacitors adapted to be alternatively switched on through a switch and to be charged through a photoresistor.

The invention will now be described more fully by means of a few embodiments with reference to the accompanying drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates the circuit diagram of one embodied form of the invention including a controlled semiconductor rectifier.

FIG. 2 illustrates the circuit diagram of another embodied form of the invention including two controlled semiconductor rectifiers in parallel connection.

DESCRIPTION OF SPECIFIC EMBODIMENTS The following disclosure is offered for public dissemination in return for the grant of a patent. Although it is detailed to ensure adequacy and aid understanding. The claims at the end hereof are intended as the chief aid toward this purpose as it is these that meet the requirement of pointing out the parts, improvements, or combinations in which the inventive concepts are found.

According to FIG. 1 a storage capacitor is charged by a supply voltage (created in known manner) across input terminals 10, 12. The normal discharge circuit of a flash tube 16 includes a resistor 18, a resistor 20 and a controlled semiconductor rectifier 22. The flash tube 16 has an ignition electrode 24 which may be provided with a high-voltage ignition pulse by an ignition coil (ignition transformer) 26. To this end, an ignition capacitor 28 is provided which, when an ignition switch 30 is closed, discharges through the primary winding of the ignition transformer 26. The ignition capacitor 28 is charged by the supply voltage through a voltage divider comprised of resistors 32, 34, and 36, the ignition capacitor 28 and the primary winding of the ignition transformer 26. When the ignition switch 30 is closed, the potential at point 38 increases.

A capacitor 40 in parallel with the resistor 32 is also charged to a part of the supply voltage. This capacitor 40 is connected with the ignition electrode of the controlled semiconductor rectifier 22 through a trigger diode 42 and a current-limiting resistor 44. When the ignition contact 30 is open, the trigger diode 42 is blocked. When the contact 30 is first closed and hence, the potential at point 38 increases, the trigger diode 42 becomes conducting and there is an ignition of the controlled semiconductor rectifier 22 by the discharge of the capacitor 40.

An auxiliary capacitor 46 is provided in an electric circuit branching off between the controlled semiconductor rectifier 22 and the flash tube 16. This branch circuit includes a resistor 48, a second controlled semiconductor rectifier 50 and terminates again in the discharge circuit of the flash tube 16 between the resistors 18 and 20. Moreover, through decoupling resistors 52 and 54, the capacitor 46 connects to the supply voltage so that it charges to the level of the supply voltage.

Connected across the resistor 20 is a light integrator circuit. This circuit is made up of a diode 56, a photoresistor 58 and a capacitor 60 having an adjustable resistor 62 in parallel therewith.

The point between the photoresistor 58 and the capacitor 60 is connected with the grid electrode of a thyristortetrode 64. An auxiliary capacitor 66 is charged by the supply voltage to a partial voltage by means of a voltage divider comprised of the resistors 68 and 70. When the thyristor-tetrode conducts, the capacitor 66 discharges through the tetrode 64 and a resistor 72. Thereby, an ignition voltage is supplied to the control electrode of the second controlled rectifier 50 through a resistor 74.

The operation of the arrangement as indicated is as follows:

Upon closing the ignition switch 30, an ignition pulse is supplied to the ignition electrode 24 of the flash tube 16. Simultaneously, the potential in point 38 increases so that the trigger diode 42 conducts. The capacitor 40 discharges through the trigger diode to ignite the controlled rectifier 22. Now, the normal flash discharge is effected from the storage capacitor 14 through the flash tube 16, and a voltage drop appears across the resistor 20. This voltage charges the capacitor 60 through the photoresistor 58 which regulates the charging current; i.e, the greater the light flux impinging on the photoresistor, the greater will be the charging current. Thus, the charge on capacitor 60 corresponds at least approximately to the integral of the light flux when this light flux integral reaches a desired value, the charge on capacitor 60 initiates conduction of the thyristortetrode 64. The capacitor 66 then discharges and ignites the second controlled rectifier 50. Through this second controlled rectifier 50 the capacitor 46 is practically connected in series to the storage capacitor 14. Now, across the part of the discharge circuit comprised of the resistor 20 and the controlled-rectifier 22 the capacitor 46 applies a voltage of such a polarity, that is plus on the left of controlled rectifier 22 and minus on its right, which is opposed to the polarity of the voltage applied during the normal discharge of capacitor 14. Thereby, the controlled rectifier 22 is quenched. A charge in an opposite direction of the capacitor 46 is additionally effected through the flash tube 16, and then the flash discharge is quenched. The capacity of the auxiliary capacitor 46 may be designed substantially smaller than the capacity of the storage capacitor 14. Once, the controlled semiconductor rectifier 22 is quenched, it remains quenched so that also if residual ions exist in the flash tube 16, the flash discharge is not started again. In that the light flux integration circuit 58, 60 is supplied by the voltage drop across a resistor in the flash discharge circuit, it is ensured that the integration only starts with the beginning of the flash discharge.

In the embodiment according to FIG. 2, the supply voltage is applied to the input terminals 10, 12 and charges a storage capacitor 14. The storage capacitor 14 discharges through the flash tube 16. In the discharge circuit are resistors 18, 20, as well as two controlled semiconductor rectifiers (thyristors) 22, 22' connected in parallel'and each in series with an inductive reactor 19 and 19', respectively. The flash tube 16 is ignited by a high-voltage pulse applied to the ignition electrode 24. This high-voltage pulse is created when the ignition switch 30 is closed. This causes a capacitor 28 (charged through the voltage divider comprising the resistors 32, 34, and 36,) to discharge through the primary winding 36 of the ignition transformer. The secondary winding 26 of the transformer is connected to the ignition electrode 24.

A voltage drop exists across the resistors 32 and 34, and this charges a capacitor 41 through resistors 37 and 39. The connection point between the resistor 37 and the capacitor 41 connects to the control electrode of a controlled semiconductor rectifier 43. The controlled semiconductor rectifier 43 connects to a capacitor 47 together with a series-resistor 45. Capacitor 47 is charged through a resistor 49 by the voltage across the resistor 32. The connection point between the controlled semiconductor rectifier 43 and the resistor 45 connects through resistors 51, 53 to the control electrodes of the two controlled semiconductor rectifiers 22 and 22', respectively.

When the flash tube 16 is ignited by closing of the switch 30 by means of a pulse applied to the control electrode 24, the same closing of the switch 30 simultaneously raises the potential of the control electrode of the controlled semiconductor rectifier 43 towards the positive. The capacitor 41 provides the current required to ignite the controlled semiconductor rectifier 43. When the controlled semiconductor rectifier 43 ignites, a current pulse is supplied through it by the capacitor 47. This current pulse is applied to the control electrodes of the controlled semiconductor rectifiers 22 and 22', so that the latter are ignited simultaneously with the flash tube 16. Differences in the ignition point of the controlled semiconductor rectifiers 22 and 22' are balanced by the inductive reactorsl9 and 19 so that also at the moment where the flash discharge starts, no'overload on one of the controlled semiconductor rectifiers can occur.

In the arrangement according to this invention, the quenching circuit includes a second pair of controlled semiconductor rectifiers 50, 50. The controlled semiconductor rectifier 50 is in an electric circuit which originates from the point between the controlled semiconductor rectifier 22 and the reactor 19 and includes a capacitor 46,. a resistor 48 and a reactor 55. From the controlled semiconductor rectifier 50 this electric circuit then leads to the point between the resistors 18 and 20.

The controlled semiconductor rectifier S0" is in an electric circuit originating from the point between the controlled semiconductor rectifier 22 amd the reactor 19 and including, a capacitor 46, a resistor 48 and a reactor 55. This electric circuit then also leads from the controlled semiconductor rectifier 50' to the point between the resistors 18. and 20.

The capacitors 46 and46 are charged by the supply voltage through decoupling resistors, and that is on the one hand through the common resistor 52as well as the inductive reactors 19 and 19 (negligible for this charge), and on the other hand through resistors 54 and 54', respectively.

The control of the controlled semiconductor rectifiers 50 and 507 is efl'ected through an integrating element comprising a photoresistor 58, a diode 84 as well as switchably a pair of capacitors 60 and 62, respectively. Each of the capacitors has in parallel connection thereto a resistor and 92, respectively. Switching is accomplished by means of a switch 94. A capacitor is charged by the supply voltage'through resistors 96 and 98. The voltage across the capacitor 100 is stabilized'by a Zener-diode 102 which is connected in pare]- lel with it and the resistor 98. Another controlled semiconductor rectifier 104 connects to the capacitor 100 in series to a resistor 106. The control electrode of the controlled semiconductor rectifier 104 is connected through a line 108 to the moving contact of the switch 94 across which, in an operating position thereof, the voltage is derived at one of the integration capacitors 60 and 62, respectively. The point between the controlled semiconductor rectifier 104 and the resistor 106 is connected through a line 110 and two resistors 112 and 114, respectively, with the control electrodes of the controlled semiconductor rectifiers 50 and 50', re-

spectively.

The arrangement of FIG. 2 operates as follows:

After ignition of the flash tube, the light reflected by the object impinges upon the photoresistor 58. The photoresistor 58 and the switched-on capacitor 60 (or 62) have a voltage applied thereto, which voltage is that appearing (IR drop) across the resistor 20 during flash discharge by reason of the; current flow through the flash tube 16. The capacitor, for instance 60, is charged by this voltage at a rate controlled by the photoresistor 58. At a specific integral of the light flux, the controlled rectifier 104 is ignited by the voltage across the capacitor 60. Due to this ignition, a current pulse is supplied to the ignition electrodes of the controlled rectifiers50 and 50 by the capacitor 100. Thereby, the capacitors 46 and 46 are discharged through the resistor 20 to produce a voltage drop thereacross. This voltage drop changes the polarity of the voltage across the controlled rectifiers 22and 22', respectively. Therefore, the controlled rectifiers 22 and'22 become nonconductive and after a releasing time of about 12 mi- .croseconds remain in a nonconductive state after discharge of the capacitors 46 and 46', respectively. Then, the capacitors 46 and 46' are additionally charged in an opposite direction through the discharge tube 16 from the capacitor 14, and then also the tube 16 is quenched.

Advantageously, the resistor 18 is large with respect to the resistor 20. Thereby, it is attained that the electric circuit parallel to the normal discharge circuit of the capacitors 46 and 46', through the reactors 19 and 19', respectively, the tube 16, the capacitor 14 and the resistor 18 is comparably high-ohmic.

The relatively high-ohmic resistors 90 and 92 provide for a respective discharge of the capacitors 60 and 62, respectively at the beginning of the in-tegration.

I claim:

1. In an electronic flashligh unit for use with a direct current supply voltage, comprising a discharge voltage capacitor charged from said supply voltage, a gas filled flash tube connected to said capacitor and having an ignition electrode for initiating a flash discharge, an ignition device connected to said electrode to energize said electrode for igniting said flash tube, a photoelectric detector controlled by reflected light from said flash tube, an integrating element connected to the detector for at least approximately integrating the light flux, and quenching means for quenching the flash discharge when a given light flux integral is reached, controlled semiconductor rectifier means connected in series to the flash tube and the capacitor, and means connected to said device and to said semiconductor rectifier means to ignite the rectifier means simultaneously with the ignition of the flash tube, said quenching means being connected to the controlled semiconductor rectifier means to temporarily change the polarity of the voltage across said rectifier means to thereby turn off the rectifier means and thus quench the flash discharge, the improvement comprising:

said controlled rectifier means including a pair of controlled semiconductor rectifiers circuit means forming a part of said series circuit and comprising two parallel circuits each of which includes a respective one of said controlled rectifiers, said circuit means also including a respective inductive reactor in each of said parallel circuits in series with the respective controlled rectifier in the circuit. 2. In an electronic flashlight unit as claimed in claim I, wherein the quenching means includes an auxiliary capacitor, means including decoupling resistors connected to said supply voltage and said capacitor to charge said capacitor, a third controlled rectifier connected to and controlled by the integrating elements, said third controlled rectifier connecting said capacitor to a part of the discharge circuit including the controlled rectifier means, with a polarity opposed to the polarity of the voltage appearing across this part of the discharge circuit during normal discharge through the flash tube. 3. In an electronic flashlight unit as claimed in claim wherein the photoelectric detector and the integrating element are a photoresistor and a second capacitor, including a resistor in the discharge circuit, said resistor, photoresistor and second capacitor being connected in series, and a thyristor-tetrode connected to control the energizing of the third controlled semiconductor rectifier. 4. In an electronic flashlight unit as claimed in claim 3, wherein a third capacitor is connected to the thyristor-tetrode to effect the ignition of the third semiconductor rectifier. 5. In an electronic flashlight unit as claimed in claim 4, including a voltage divider across the supply voltage, a fourth capacitor connected to be charged from the voltage divider, a trigger diode connecting the fourth capacitor to the ignition electrode of the controlled semiconductor rectifier means, and an ignition switch short circuiting part of the voltage divider to raise the potential of the fourth capacitor to a potential sufficient for current passage through the trigger diode. 6. In an electronic flashlight unit as claimed in claim 5, including an ignition transformer having a primary and a secondary, said secondary being connected to the ignition electrode of the flash tube, the primary being connected to said fourth capacitor.

7. In an electronic flashlight unit as claimed in claim 1, wherein the quenching means includes a second pair of controlled semiconductor rectifiers, a pair of capacitors, and a second pair of inductive reactors, one of said second pair of semiconductor rectifiers being connected to one of said second pair of inductive reactors and one of said pair of capacitors with the three being connected in parallel to one of the first mentioned semiconductor rectifiers, the other of the second pair of semiconductor rectifiers being connected to the other of the second pair of inductive reactors and the other of said pair of capacitors with the three being connected in parallel to the second of the first mentioned semiconductor rectifiers, and means including decouplingresistors connecting said pair of capacitors to saidsupply voltage, said second pair of semiconductor rectifiers being connected to the integrating element to be simultaneously ignited by the integrating element when a predetermined light flux integral is reached. 8. In an electronic flashlight unit as claimed in claim 7, wherein each capacitor of the quenching circuit is connected between the respective semiconductor rectifier in the discharge circuit and the reactor of that respective rectifier. 9. In an electronic flashlight unit as claimed in claim 7, wherein the quenching circuit includes another semiconductor rectifier, a resistor for said other rectifier and connected in series thereto and defining a connection point therebetween, means connecting said connection point with the control electrodes of the second pair of semiconductor rectifiers, a capacitor for said other rectifier and connected to the resistor for the other rectifier, means connecting the latter capacitor to the supply voltage for charging the same, and integrating means connected to said other semiconductor rectifier for controlling the same. 10. In an electronic flashlight unit as claimed in claim 9, wherein a Zener diode connected to the last mentioned capacitor to stabilize the voltage of the same. 1 1. In an electronic flashlight unit as claimed in claim 9, wherein 50 said integrating means including a plurality of capacitors, and a multiposition switch by which the capacitors may alternatively be made effective. 12. In an electronic flashlight unit as claimed in claim 8, wherein the quenching circuit includes another semiconductor rectifier, a resistor for said other rectifier and connected in series thereto and defining a connection point therebetween, means connecting said connection point with the control electrodes of the second pair of semiconductor rectifiers, a capacitor for said other rectifier and connected to the resistor for the other rectifier, means connecting the latter capacitor to the supply voltage for charging the same, and integrating means connected to said other semiconductor rectifier for controlling the same. 13. In an electronic flashlight unit as claimed in claim 12, wherein 3,808,500 9 10 a Zener diode connected to the'last mentioned ca said integrating means includingaplurality of capaci' pacitor to stabilize the voltage of the same. tors, and a multiposition switch by which the ca- 14. In an electronic flashlight unit as claimed in claim pacitors may alternatively be made effective. 12, wherein r I 

1. In an electronic flashligh unit for use with a direct current supply voltage, comprising a discharge voltage capacitor charged from said supply voltage, a gas filled flash tube connected to said capacitor and having an ignition electrode for initiating a flash discharge, an ignition device connected to said electrode to energize said electrode for igniting said flash tube, a photoelectric detector controlled by reflected light from said flash tube, an integrating element connected to the detector for at least approximately integrating the light flux, and quenching means for quenching the flash discharge when a given light flux integral is reached, controlled semiconductor rectifier means connected in series to the flash tube and the capacitor, and means connected to said device and to said semiconductor rectifier means to ignite the rectifier means simultaneously with the ignition of the flash tube, said quenching means being connected to the controlled semiconductor rectifier means to temporarily change the polarity of the voltage across said rectifier means to thereby turn off the rectifier means and thus quench the flash discharge, the improvement comprising: said controlled rectifier means including a pair of controlled semiconductor rectifiers circuit means forming a part of said series circuit and comprising two parallel circuits each of which includes a respective one of said controlled rectifiers, said circuit means also including a respective inductive reactor in each of said parallel circuits in series with the respective controlled rectifier in the circuit.
 2. In an electronic flashlight unit as claimed in claim 1, wherein the quenchinG means includes an auxiliary capacitor, means including decoupling resistors connected to said supply voltage and said capacitor to charge said capacitor, a third controlled rectifier connected to and controlled by the integrating elements, said third controlled rectifier connecting said capacitor to a part of the discharge circuit including the controlled rectifier means, with a polarity opposed to the polarity of the voltage appearing across this part of the discharge circuit during normal discharge through the flash tube.
 3. In an electronic flashlight unit as claimed in claim 2, wherein the photoelectric detector and the integrating element are a photoresistor and a second capacitor, including a resistor in the discharge circuit, said resistor, photoresistor and second capacitor being connected in series, and a thyristor-tetrode connected to control the energizing of the third controlled semiconductor rectifier.
 4. In an electronic flashlight unit as claimed in claim 3, wherein a third capacitor is connected to the thyristor-tetrode to effect the ignition of the third semiconductor rectifier.
 5. In an electronic flashlight unit as claimed in claim 4, including a voltage divider across the supply voltage, a fourth capacitor connected to be charged from the voltage divider, a trigger diode connecting the fourth capacitor to the ignition electrode of the controlled semiconductor rectifier means, and an ignition switch short circuiting part of the voltage divider to raise the potential of the fourth capacitor to a potential sufficient for current passage through the trigger diode.
 6. In an electronic flashlight unit as claimed in claim 5, including an ignition transformer having a primary and a secondary, said secondary being connected to the ignition electrode of the flash tube, the primary being connected to said fourth capacitor.
 7. In an electronic flashlight unit as claimed in claim 1, wherein the quenching means includes a second pair of controlled semiconductor rectifiers, a pair of capacitors, and a second pair of inductive reactors, one of said second pair of semiconductor rectifiers being connected to one of said second pair of inductive reactors and one of said pair of capacitors with the three being connected in parallel to one of the first mentioned semiconductor rectifiers, the other of the second pair of semiconductor rectifiers being connected to the other of the second pair of inductive reactors and the other of said pair of capacitors with the three being connected in parallel to the second of the first mentioned semiconductor rectifiers, and means including decoupling resistors connecting said pair of capacitors to said supply voltage, said second pair of semiconductor rectifiers being connected to the integrating element to be simultaneously ignited by the integrating element when a predetermined light flux integral is reached.
 8. In an electronic flashlight unit as claimed in claim 7, wherein each capacitor of the quenching circuit is connected between the respective semiconductor rectifier in the discharge circuit and the reactor of that respective rectifier.
 9. In an electronic flashlight unit as claimed in claim 7, wherein the quenching circuit includes another semiconductor rectifier, a resistor for said other rectifier and connected in series thereto and defining a connection point therebetween, means connecting said connection point with the control electrodes of the second pair of semiconductor rectifiers, a capacitor for said other rectifier and connected to the resistor for the other rectifier, means connecting the latter capacitor to the supply voltage for charging the same, and integrating means connected to said other semiconductor rectifier for controlling the same.
 10. In an electronic flashlight unit as claimed in claim 9, wherein a Zener diode connected to the last mentioned capacitor to stabilize the voltage of the same.
 11. In an electronic flashlight unit as claimed in claim 9, wherein said integrating means including a plurality of capacitors, and a multiposition switch by which the capacitors may alternatively be made effective.
 12. In an electronic flashlight unit as claimed in claim 8, wherein the quenching circuit includes another semiconductor rectifier, a resistor for said other rectifier and connected in series thereto and defining a connection point therebetween, means connecting said connection point with the control electrodes of the second pair of semiconductor rectifiers, a capacitor for said other rectifier and connected to the resistor for the other rectifier, means connecting the latter capacitor to the supply voltage for charging the same, and integrating means connected to said other semiconductor rectifier for controlling the same.
 13. In an electronic flashlight unit as claimed in claim 12, wherein a Zener diode connected to the last mentioned capacitor to stabilize the voltage of the same.
 14. In an electronic flashlight unit as claimed in claim 12, wherein said integrating means including a plurality of capacitors, and a multiposition switch by which the capacitors may alternatively be made effective. 